Saccade-related cells in the monkey superior colliculus (SC) can be divided into two general categories, burst cells and buildup cells. Among their distinguishing features is the activity during saccades: activity int he buildup cells spreads across the layer containing these cells; that does not happen for the burst cells. This difference in activity of these cells led to the suggestion that they play different roles in the generation of saccades. In a feedback control model of saccade generation, the SC lies in the feedback loop and provides two outputs; the burst cells provide the desired amplitude of the saccide; the buildup cells convey information about how far the saccade has progressed by using the spread of activity in the buildup cells as a spatial integrator. The buildup cells therefore should control the trajectory of the saccade according to the spread of activity across the SC during the generation of the saccade. We tested whether modification of the spread of activity in the SC buildup cells changes the trajectory of the saccade, by using injections of a GABAergic drug (muscimol) to reversibly alter the activity of the SC cells. We injected muscimol into one area of the SC to disrupt the rostral spread of activity int he buildup cells. We found alterations of the saccade trajectory; the saccades were curved but reached the target. For saccades whose amplitudes were largely unaltered, the saccade deviated from the nearly straight line that it took to the target before the lesion. This deflection started soon after the saccade began, but the saccade then changed direction to bring the eye on target. This is consistent with the hypothesis that the spread of activity among the buildup cells contributes to the control of saccades, including the trajectory of the saccade.